Water absorbent web and its production

ABSTRACT

A web which is soft and rapidly and highly water absorbent when both wet and dry is produced by sandwiching under pressure a layer of cellulose pulp fiber reinforced, foamed viscose between thin fleeces of unbonded cotton fibers and regenerating the viscose cellulose. The product is a reticulated matrix of regenerated cellulose and dispersed pulp fibers with the fleece fibers embedded in the opposite faces of the regenerated cellulose layer.

Pulitzer et al. 1451 Apr. 1, 1972 154] WATER ABSORBENT WEB AND ITS2,069,771 2/1937 Pascoe et al. ..162/164 x PRODUCTION 2,076,594 4/1937Richter ..260/217 2,079,993 5/1937 Hans ..260/217 x [72] Inventors:Alfred Pulitzer, Falrview Park; Galrb-Bey 2 104 57 H1933 Scott a D"ml/269 X Mam Alibeflwifi Lakewqod; PaO-Chi 2,182,188 12/1939 Walter 161/269 x Wang, y vlllage, all of 01119 2,257,576 9/1941 Robinson ..161/2696 2,744,292 5/1956 Schlosser et al. ..161/269 X [73] i Nylmge CmpmmnCleveland Ohm 3,171,773 3/1965 Estes et a1 ..161/269 x 22 Filed: July23, 1969 3,366,532 1/1968 Maskey et al. ..161/269 x [211 App! NO':844l53 7 Primary Examiner-Harold Ansher Attorney-Milton H. Gross 52 us.c1 ..l56/78,117/144, 156/298,

161/156, 161/161, 260/217 57 ABSTRACT 51 lnt.Cl. ..B32b 31/06 B32b 23/06[58] Field 61 Search ..161/269,151,156,159-161; A Web and rapdly andhghly water absorbent 156/78 79 62 4 279 280 26O/217 when both wet anddry is produced by sandwiching under 4 pressure a layer of cellulosepulp fiber reinforced, foamed viscose between thin fleeces of unbondedcotton fibers and regenerating the viscose cellulose. The product is areticulated [56] References Clted matrix of regenerated cellulose anddispersed pulp fibers with UNITED STATES PATENTS the fleece fibersembedded in the opposite faces of the regenerated cellulose layer.3,546,060 12/1970 Hoppe et a1 ..161/159 X 3,578,544 5/197] Thorsrud..l56/78X 7Claims,NoDrawings WATER ABSORBENT WEB AND ITS PRODUCTIONBACKGROUND OF THE INVENTION The present invention relates generally toimprovements in wiping, washing and cleaning articles and it relatesparticularly to an improved soft, highly water absorbent, web or clothand to an improved method for producing the same.

Wiping and cleaning webs are broadly of two types, the paper towel ornapkin type which is generally formed of randomly oriented woodcellulose fibers in a relatively compact non-woven state produced onconventional paper producing equipment and the woven or knitted clothtype which is conventionally formed of cotton fibers. The conventionalwiping and cleaning webs possess numerous drawbacks and disadvantageswhich characterize the particular type of web. Thus, the woven orknitted cotton cloth is generally coarse and commonly not lint free andare too expensive to be considered disposable so that for economicreasons they must be regularly laundered. The paper towel, on the otherhand, is likewise coarse, of low water absorption, and slow watertake-up and very weak both in a dry and wet state. These webs have beentreated with polymeric resins to increase their wet strength but suchtreatment increases the cost of the product and reduces its waterabsorption qualities and increases its courseness. It is thus clear thatthe conventional wiping and cleaning webs leave something to be desiredand generally represent acompromise.

Numerous structures have heretofore been proposed in attempts to avoidthe disadvantages of the conventional cloth and paper webs but thesestructures fail to remedy the important defects thereof. A laminateconsisting of two or more tissue paper webs cemented together byregenerated cellulose derived from intermediate layers of foamed viscosehas been described but this product is relatively hard and stiff,particularly when dry, and possesses a slow water take up. It has also ibeen suggested to laminate carded cotton fleeces with resin foams butthe resulting product is of low water absorption and permeability.Various other composite products have been proposed which do not satisfythe long felt need for an inexpensive web of high absorption and rapidtake-up of water, which web is soft and strong when both wet and dry.

SUMMARY OF THE INVENTION It is a principal object of the presentinvention to provide an improved cleaning and wiping article and animproved method of producing the same.

Another object of the present invention is to provide an improvedcleaning and wiping cloth and an improved method of producing the same.Still another object of the present invention is to provide an improveddisposable highly water absorbent cleaning and wiping cloth which isvery soft and possesses rapid water take-up and great strength both in awet and dry State.

A further object of the present invention is to provide an article ofthe above nature characterized by its low cost, versatility, convenienceof use and attractive appearance.

The above and other objects of the present invention will becomeapparent from a reading of the following description.

It has been discovered that a laminate of a reticulated regeneratedcellulose layer and a layer of independently movable cellulose fibers inwhich the cellulose fibers at the layer interface are imbedded in theregenerated cellulose layer possesses numerous highly desirablecharacteristics and features. Among these are a high water absorptioncapacity, a rapid water take-up and great softness when wet and dry anda very high wet and dry strength. The improved article also possesses ahigh abrasion and wear resistance, is lint free, inexpensive, so as tobe economically disposable, and possesses numerous other advantages.

In a sense the present invention contemplates the provision of a highlywater absorbent web, sheet or slab material which is soft, pliable andof high strength when both wet and dry and comprises a reticulatedmatrix of regenerated cellulose,

preferably containing cellulose pulp fibers, sandwiched between oppositelayers of non-woven cellulose fibers embedded in the opposite faces ofthe regenerated cellulose matrix.

The web or sheet is of a thickness of 0.15 millimeter to 5 millimetersor more with the weight of each of the outer fiber layers being between4 to 60 grams per square meter and the outer fiber layers constitutebetween 2 percent and percent by weight of the dry product. Theregenerated cellulose constitutes at least 15 percent by weight of thematrix, which may contain cellulose reinforcing fibers, andadvantageously in excess of 20 percent thereof and preferablyconstitutes between 15 percent and percent by weight of the dry endproduct. Where the matrix contains only a small amount of reinforcingfibers the reticulated matrix may be to a large extent defined by ahighly porous or reticulated structure and where a large proportion ofreinforcing fibers are employed the matrix may be defined by a threedimensional fiber network bonded by the regenerated cellulose.

The reinforcing fibers are advantageously of relatively small staplelength preferably averaging between 1.5 mm and 4 mm, although longeraverage staple lengths may be employed whereas the outer fiber layersare advantageously of relatively large staple length preferablyaveraging between 10 and 60 mm. Advantageously the matrix reinforcingfibers are derived from a cellulose pulp, for example a wood pulp, whilethe outer layer fibers are advantageously cotton or rayon fibers whichare for the most part randomly oriented and preferably freely and threedimensionally and independently interrelated such as of the nature of afleece or web of randomly oriented fibers, for example of the natureproduced by the Rando web forming process in the known manner.

The improved method for producing the present product comprises thesteps of forming a foamed preferably fiber reinforced viscose,sandwiching a layer of the foamed viscose between opposite cellulosefiber layers, compressing the laminate and thereafter regenerating thecellulose in the viscose. The foaming is advantageously primarilyeffected by admixing the Viscose, reinforcing fibers and a surfactantand whipping the resultant mixture to incorporate and disperse airtherein and reduce its specific gravity which is initially about 1.3, tobetween 0.6 and 0.15. It has been found that the viscose should possessa high alkalinity as compared to the normal alkalinity of viscose, thatis it should possess a ratio of sodium hydroxide to viscose celluloseexceeding 0.9: 1.0, and an alkalinity corresponding to a ratio of sodiumhydroxide to the viscose cellulose and reinforcing cellulose fibersexceeding 07:10. The viscose cellulose is preferably 2 to 10 percent byweight of the viscose and the alkalinity is between 1.8 percent and 25.percent. The high alkalinity permits the production of a product with ahigh proportion of regenerated cellulose possessing great softness andpliability both wet and dry.

The laminate of outer fibrous webs and inner viscose foam may becompressed by passing it between suitably biased squeeze rolls orbetween belts or webs which are squeezed together. The compressedlaminate is then passed through a suitable coagulating and regeneratingbath, for example, an aqueous solution containing 10 to 28 percentsodium sulfate and 0.5 to 2.5 percent sulphuric acid, advantageously atan elevated temperature, preferably between 90 and C to coagulate andregenerate the viscose and the resulting product is then washed,bleached and dried. It has been found that the use of high bathtemperature results not only in a greater coagulation and regenerationspeed but also in a softer product of reduced density and otherdesirable properties.

Where a relatively thick product is desired it is advantageous to admixwith the foamed viscose sodium sulfate decahydrate crystals. Thesecrystals may have an average size up to about inch and may constitute upto 8 times the weight of the viscose and the reinforcing fiberscontained therein. Moreover, the improved product may contain more thantwo fibrous layers, for example, three or more, and such product isproduced by forming a laminate of alternate layers of fibrous webs andviscose foam with the fibrous webs forming the outer layers as well asone or more inner layers and then proceeding in the manner describedabove.

A highly advantageous method of forming the laminate of fibrous outerlayers and viscose foam matrix layers is to deposit a first layer ofrandomly oriented fibers onto a substrate by means of a Rondo webforming apparatus, deposit a layer of the foamed viscose mixture ontothe first layer and deposit by means of the Rondo machine a second layerof randomly oriented cellulose fibers onto the viscose foam layer. Thesubstrate may be a perforate belt or screen and the laminate iscompressed while being advanced on the substrate belt by means of anupper superimposed belt or pressure roller. The foamed viscose layer isof a thickness depending on that of the desired end product.

The improved product of the present invention possesses an extremelyfast water take-up, a very high water retention, is highly porous, andis soft and strong in both a dry and wet state and is lint free andhighly abrasion and wear resistant. It is boilable and launderable, iseasily disinfected and sterilized and may be dyed, printed, sewn, glued,cemented and otherwise treated and handled. While it is highly suitableas a wiping and wash cloth it possesses numerous other applications. Itis highly useful for clothing, bed linens, surgical pads, filters, andother applications and may be impregnated with many active materials.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples aregiven merely by way of illustration of the present invention.

EXAMPLE I There was prepared in the conventional manner viscosecontaining 4.25 percent cellulose, 15.8 percent sodium hydroxide and1.85 percent sulphur originating in the CS employed in the viscosepreparation. The viscose had a viscosity of 8 seconds as determined inthe known manner with a $4; inch steel ball and a 20 centimeter fall.Two percent by weight of the surfactant dienthanol amine of capric acid(Nopco GLN) was admixed with the viscose.

Finely divided cellulose pulp fibers are produced by disintegrating in ahammer mill a 91 percent alpha cellulose bleached Kraft wood pulp(Buckeye Cellulose E1). The cellulose fibers possessed the followingscreen analysis:

TE 14 TF 48.4% TE 28 TF 3 3 .4% TE 48 TF 9.9% TE 100 TF 4.7% TE 100 TFTen pounds of the surfactant containing viscose was mixed in a kneaderfor l minutes to partially foam and increase the volume of the viscose.Thereafter, 1.25 pounds of the disintegrated pulp was added to theviscose and the mixing continued for another 45 minutes during which themain foaming occurred and the foamed mass reached a specific gravity of0.34.

A first fleece of randomly oriented loose cotton fibers was deposited inthe known manner on a Teflon coated screen, the fleece having a weightof 15 grams per square meter. A layer of the foamed viscose mass of athickness corresponding to about 600 grams per square meter wasuniformly deposited on the first fleece and a second fleece, similar tothe first fleece, was then deposited on the viscose mass layer. A secondTeflon coated screen was deposited on the viscose fleece laminate andthe assembly was advanced between a pair of rubber coated squeezerollers at a pressure of about 30 pounds per square inch.

The squeezed screen and laminate assembly was then directed into acoagulation and regeneration bath at l00 C and containing 2 percentsulfuric acid and 26 percent sodium sulfate. After immersion in the bathfor three minutes the assembly is removed and the laminate separatedfrom the screens and subjected to a suitable after treatment includingthe steps of desulfurizing, bleaching, antichlor treatment, washing anddrying.

The resulting product was soft when wet or dry and possessed a very highwet and dry strength and consisted of 18.7 percent regeneratedcellulose, 56.3 pulp fibers, 25 percent cotton fibers and had a weightof 120 grams per square meter.

EXAMPLE I] The procedure of Example I was followed in which the viscosecontained 6.2 percent cellulose, 7.3 percent sodium hydroxide and 2.7percent sulfur and had a viscosity of 27 seconds. The foamed masscontained 2.6 percent of the surfactant and 0.22 pound of thedisintegrated pulp fibers in ten pounds of the viscose. The outer cottonwebs and the viscose mass layer were compressed under four pounds persquare inch pressure. In all other respects the method of Example I wasfollowed.

The resulting products contained 31.5 percent of the outer cotton webs,51.5 percent regenerated cellulose and 17.0 percent pulp fibers andweighed grams per square meter. It had a wet strength of 8.8 pounds perinch, a water absorption of 1840 percent and was soft and supple in botha wet and dry state.

While there have been described preferred embodiments of the presentinvention is is apparent that numerous alterations, omissions andadditions may be made without departing from the spirit thereof.

We claim:

1. The method of producing a water absorbent material comprising forminga viscose foam having a ratio of sodium hydroxide to cellulose exceeding0.9:l.0, sandwiching a layer of said viscose foam under pressure betweentwo layers of randomly distributed cellulose fibers having an averagestaple length exceeding 10 mm and thereafter regenerating the cellulosein said viscose.

2. The method of producing a soft water absorbent product comprisingforming a foamed viscose having an alkalinity corresponding to a ratioof sodium hydroxide to the cellulose dissolved in said viscose exceeding0.9: l .0, laminating a layer of said foamed viscose between opposinglayers of fibers and regenerating the cellulose in said viscose.

3. The method of claim 2 wherein said viscose foam contains a surfactantand reinforcing fibers dispersed and undissolved in said viscose.

4. The method of claim 3 wherein said foamed mixture is produced bywhipping air into a mixture of said viscose, reinforcing fibers andsurfactant.

5. The method of claim 3 wherein said cellulose is regenerated byexposing said laminate to an acid bath at an elevated temperature.

6. The method of claim 3 wherein said foamed mixture has a specificgravity of 0.6 to 0.15.

7. The method of claim 3 comprising depositing a first layer of randomlyoriented cellulose fibers on a substrate, depositing a layer of saidfoamed mixture on said first layer, depositing a second layer ofrandomly oriented cellulose fibers on said foamed mixture layer, andthen compressing said layers.

2. The method of producing a soft water absorbent product comprisingforming a foamed viscose having an alkalinity corresponding to a ratioof sodium hydroxide to the cellulose dissolved in said viscose exceeding0.9:1.0, laminating a layer of said foamed viscose between opposinglayers of fibeRs and regenerating the cellulose in said viscose.
 3. Themethod of claim 2 wherein said viscose foam contains a surfactant andreinforcing fibers dispersed and undissolved in said viscose.
 4. Themethod of claim 3 wherein said foamed mixture is produced by whippingair into a mixture of said viscose, reinforcing fibers and surfactant.5. The method of claim 3 wherein said cellulose is regenerated byexposing said laminate to an acid bath at an elevated temperature. 6.The method of claim 3 wherein said foamed mixture has a specific gravityof 0.6 to 0.15.
 7. The method of claim 3 comprising depositing a firstlayer of randomly oriented cellulose fibers on a substrate, depositing alayer of said foamed mixture on said first layer, depositing a secondlayer of randomly oriented cellulose fibers on said foamed mixturelayer, and then compressing said layers.